A conventional optical disk player, which reproduces video and/or audio signals recorded on an optical disk and outputs them through a display and/or a speaker, includes a CDP(Compact Disk Player), an LDP(Laser Disk Player), a CDGP(Compact Disk Graphic Player) and the like. The CDP is typically an apparatus capable of reproducing audio signals only; and both the LDP and the CDGP are apparatus capable of reproducing video as well as audio signals simultaneously. A VCDP(Video Compact Disk Player) is also capable of reproducing both video and audio signals.
These disk players are becoming more and more popular because of their high-performance characteristics, e.g., high S/N ratio, low noise, little distortion and no ghost.
In some applications such as a motion picture film, however, the amount of data, e.g., a whole volume of data of the motion picture film, is too large to be stored on a single disk and the data has to be divided onto several disks. A disk changer can be employed to load a plurality of disks on a tray roulette thereof to reproduce the data off the plurality of disks sequentially or selectively in response to a user's instructions.
Referring to FIG. 1, there is illustrated a typical tray roulette of the disk changer capable of loading three disks at a time.
The disk changer, as shown, comprises a base 10 to support a tray roulette 11 having three dishes 14 to 16 to cradle disks loaded therein, e.g., three disks 17, 18, 19, one disk in one dish, a spindle 12 around which the tray roulette 11 rotates, a sensor 13 which is attached to the base 10 and identifies each dish and generates a code for each dish.
A unique ID(identification) code is assigned to each of the dishes 14 to 16, e.g., ID1, ID2, ID3, respectively. A target dish may be easily sorted out by using these ID codes, wherein the target dish is the one that holds the disk the user selects among the disks loaded on the tray roulette for reproducing the data recorded thereon. The sensor 13, located at a position on a line making a preset angle counterclockwise with a radial line crossing a pickup position Y, is used in sensing the ID codes, wherein the pickup position is a position where the data on the target dish is reproduced, i.e., where an optical pickup device is located to catch the data read from the target dish.
For the optical pickup device at the pickup position Y to read data from the target dish, the tray roulette revolves around its spindle 12. During the rotation, the sensor 13 checks the ID of the dish passing it by generating pulse signals representing the ID of each dish to be identified.
Turning to FIG. 2, there is illustrated a conventional tray roulette controller.
The tray roulette 11 is revolved around its spindle by a motor driver 22 which drives the motor 23 by providing appropriate power to the motor 23 under the control of a micom 21, wherein the micom is a signal processing device including a microprocessor and basic peripherals such as ROM, RAM, I/O device, etc.
As is shown in FIG. 3, while the tray roulette 11 rotates, the sensor 13 generates a single pulse A for a first dish 14, two pulses B for a second dish 15 and three pulses C for a third dish 16. The micom 21 identifies each dish by counting the number of pulses coming from the sensor 13.
Also shown in FIG. 3 is a start/end pulse signal, which consists of four consecutive pulses between each ID pulse groups A, B and C. The start/end pulse signal is used for controlling the rotation of the tray roulette 11. A set of two pulses out of the four pulses is referred to as a start code S, and another set of the two remaining pulses is called an end code E.
To check the ID of the target dish while the tray roulette rotates clockwise, the micom 21 counts the number of pulses emerging after the start code S.
Upon detection of the end code E that follows an ID code pulses, the tray roulette 11 stops rotating for the target dish to be positioned exactly at the pickup position Y.
For example, the target dish is the dish 15 whose ID is ID2. If two pulses are detected after the detection of the start code S, the ID of the dish currently approaching the pickup position Y is identified as ID2. Immediately after the detection of the end code E following the pulses for the ID2, the rotation of the tray roulette 11 is stopped. The dish whose ID is ID2, i.e., the dish 15, will be positioned for the pickup position Y.
Moreover, for the purpose of easy detection, the pulses are designed such that the pulse width of the start/end pulses and that of the ID pulses are designed to be different from each other. When the tray roulette 11 rotates at its normal speed, the pulse width of the ID pulse is, e.g., 20 msec; that of the start/end pulse is, e.g., 60 msec; and the interval between the ID pulse and the start/end pulse is maintained high, e.g., at 350 msec. Therefore, merely by checking the pulse width, it is possible to determine whether a detected pulse is the start/end pulse or the ID pulse.
Upon receiving a user's instructions to search for a target dish, the micom 21 gets the ID of the target dish, and compares the ID of the target dish with the ID of the dish currently positioned at the pickup position Y. If the result of the comparison is not equal, the micom 21 sends a drive signal to the motor driver 22 to rotate the motor 23. Once the tray roulette 11 rotates, the micom 21 detects at first the start code from the sensor 13, and then receives the ID pulse. While the tray roulette keeps rotating, it detects a falling edge of the first pulse which is the starting point of the end pulse E. Upon detecting the falling edge, it outputs a PWM(Pulse Width Modulation) signal having a predetermined duty ratio for use in reducing the rotation speed of the motor 23 to the motor driver 22, wherein the PWM signal consists of a string of consecutive pulses whose duty ratio varies.
Then, when the micom 21 detects a rising edge of the second pulse, indicating ending of the end pulse E, it outputs a reverse-polarity one-shot pulse to the motor driver 22, thus forcing the tray roulette to stop rotating, wherein the reverse-polarity one-shot pulse is used for stopping the rotation of the motor 23 to generate a torque whose direction is opposite that of the rotation.
To control the tray roulette in accordance with the conventional disk player, however, the micom 21, on the basis of the received codes from the sensor 13, identifies the received codes by counting the number of pulses in the received codes and checking the duty ratio of the pulses, compares the received codes with the code of the target dish inputted by the user, and provides the drive signal and the reverse-polarity one-shot pulse to the motor drive 22, and the like. Therefore, it is rather time consuming to go through the whole processes, which after results in a rather long search time in seeking the target dish.